The present invention relates to an intake manifold of an outboard motor.
An outboard motor includes a multiple-cylinder engine provided with an intake manifold unit (which will be called merely intake manifold or manifold, hereinlater) for distributing intake air, the flow of which is regulated by a throttle body, to the respective cylinders of the engine. Such an intake manifold is normally made of aluminum alloy. However, this time, an intake manifold having a portion downstream of a throttle body, which is made of synthetic resin, has been considered and adopted for an outboard motor for the first time by the applicant of the subject application.
Some intake manifolds are provided with IAC (idling air control) valve (which may be designated as an ISC (idling speed control valve)) for regulating a quantity of intake air when a throttle valve arranged in a throttle body is closed (i.e. during an idling state). The IAC valve is normally attached to the intake manifold through a valve holder made of sheet metal.
The intake manifold is also provided with a by-pass passage for regulating the quantity of air flowing through the IAC valve. A union made of brass is press-fit into an air inlet of the by-pass passage to reduce intake noise and to prevent the entry of seawater or the like into the intake manifold.
Moreover, in order to measure the interior pressure of the intake manifold, a pressure sampling (takeout) hole for sampling pressure is formed so as to communicate with a pressure sensor through a hose.
However, if an intake manifold made of resin is used and a sheet metal holder is used to attach the IAC valve to an intake manifold body, the edge portion of the holder contacts the surface of the intake manifold body and scrapes the resin surface thereof, thus being inconvenient.
Furthermore, in many cases, the IAC valve is fixed in a semi-floating state by an elastic element such as rubber. Due to this fact, depending on a state in which the IAC valve is attached, the IAC valve may contact an attachment bolt and the operating vibration of the IAC valve may be propagated to the intake manifold. Since such vibration tends to be easily propagated to the resin intake manifold, the vibration may cause the generation of noise.
Furthermore, it is undesirable to press-fit the brass union into the air inlet of the by-pass passage because of the disadvantageous increase in the number of parts and the increase in the number of assembling steps.
In a case where a pressure sampling hole for measuring internal pressure is formed in the intake manifold and connected to the pressure sensor through a hose, it is necessary to provide some filter means on the intake manifold so as to prevent fuel or lubricant from entering the intake manifold. This undesirably increases the number or parts and requires providing screws or the like to the intake manifold so as to attach such a filter means thereto.
An object of the present invention is to eliminate defects or drawbacks encountered in the prior art mentioned above and to provide an outboard motor intake manifold capable of reducing noise and improving assembling performance without increasing the number of parts and the number of assembling and working steps. A further object of the invention is to improve the reliability and durability of the intake manifold.
This and other objects of the present invention can be achieved by providing an intake manifold unit for an outboard motor mounting of a multiple-cylinder engine having cylinders to which intake air is distributed through the intake manifold unit, the intake manifold unit comprising:
an intake manifold body formed of a synthetic resin;
an idling air control (IAC) valve for regulating a quantity of intake air into the intake manifold body in an idling operation state;
a valve holder to which the IAC valve is operatively connected in a floating manner; and
an elastic member through which the IAC valve is mounted to the valve holder, the IAC valve, the elastic member and the valve holder being coupled integrally with each other and mounted to the intake manifold body in the floating state.
In a preferred embodiment of this aspect, the intake manifold body comprises a surge tank disposed on the downstream side of a throttle body of the intake unit and a branch extending from the surge tank and operatively connected to the engine, the surge tank being provided with a valve mounting boss to which the valve holder is mounted.
The IAC valve is provided with a flanged portion, the elastic member is composed of first and second rubbers between which the flanged portion is clamped and to which the valve holder made of metal plate is mounted in the floating manner.
The intake manifold body is formed with a pressure sampling hole, to which a pressure hose connection union is mounted, and the pressure hose connection union is operatively connected to a pressure sensor for an outboard motor in a manner that an axis of the pressure sampling hole is arranged to be offset from an axis of a passage formed in this union.
The intake manifold body is provided with a by-pass passage regulating a quantity of air flowing in the IAC valve, the by-pass passage being provided with an inlet formed so as to provide a funnel shape expanding outward, and a hood-shaped protrusion which is integrally formed above the inlet of the by-pass passage.
The intake manifold body is formed to be dividable into inside and outside shells and further provided with a valve silencer for the IAC valve, the valve silencer being divided into halves, which are integrally formed with divided inside and outside shells of the intake manifold unit, respectively. This provides an expansion chamber when the divided portions of the intake manifold body are coupled with each other.
According to the present invention of the structures mentioned above, the following advantageous functions and effects will be attained.
The outboard motor of the present invention mounts a multiple-cylinder engine having an intake manifold that distributes intake air to respective cylinders of the engine and is formed of synthetic resin, and has an IAC valve for regulating a quantity of intake air into the intake manifold in an idling state which is attached to a valve holder through an elastic element in a full floating state. Thus, the IAC valve, the elastic element and the valve holder are integrally formed with one another. The IAC valve, the elastic element and the valve holder thus integrated can be attached to the intake manifold body. Thus, the operating vibration of the IAC valve can be absorbed to thereby prevent the generation of noise in the intake manifold body, and assembling performance for assembling the parts relating to the IAC valve can be improved.
Further, a pressure sampling hole is formed in the intake manifold, and a pressure hose connection union is provided at the pressure sampling hole to connect the pressure sampling hole to a pressure sensor. An axis of the pressure sampling hole is arranged so as to be offset from an axis of a passage formed in the pressure hose connection union. Thus, it is possible to prevent fuel and lubricant from entering the pressure sensor and to reduce the number of parts and the number of assembling steps.
Moreover, according to the present invention, the by-pass passage regulating a quantity of air flowing in the IAC valve is provided for the intake manifold, an inlet of the by-pass passage is formed into a funnel shape expanding outward, and a hood-shape protrusion is integrally formed above the inlet of the by-pass passage. Accordingly, it is possible to reduce intake air noise and to prevent seawater from entering the inlet of the manifold.
Furthermore, the intake manifold is formed to be dividable, and a valve silencer for the IAC valve is formed to the intake manifold. The valve silencer is divided into halves and the respective halves are integrally formed with halves divided from the divided intake manifold to thereby form the intake manifold with an expansion chamber. Thus, it is possible to reduce the number of parts and the number of assembly steps.
The nature and further characteristic features will be made more clear from the following descriptions made with reference to the accompanying drawings.